Police: Colo. shooting suspect planned massacre

This courtroom sketch shows James Holmes being escorted by a deputy as he arrives at preliminary hearing in district court in Centennial, Colo., on Monday, Jan. 7, 2013. Investigators say Holmes opened fire during the midnight showing of the latest Batman movie on July 20, killing 12 people and wounding dozens. (AP Photo/Bill Robles, Pool) TV OUT
— AP

This courtroom sketch shows James Holmes being escorted by a deputy as he arrives at preliminary hearing in district court in Centennial, Colo., on Monday, Jan. 7, 2013. Investigators say Holmes opened fire during the midnight showing of the latest Batman movie on July 20, killing 12 people and wounding dozens. (AP Photo/Bill Robles, Pool) TV OUT
/ AP

CENTENNIAL, Colo. 
Witnesses presenting the most detailed portrait yet of last year's Aurora movie theater massacre are detailing sometimes paradoxical behavior by James Holmes, the man accused of the rampage.

At a hearing to determine whether Holmes should stand trial, detectives testified Tuesday that Holmes spent more than two months assembling an arsenal for the assault on a midnight screening of "The Dark Knight Returns."

The former neuroscience graduate student bought his tickets nearly two weeks before the July 20 massacre. He also rigged an elaborate - and potentially deadly - booby-trap system in his apartment to distract police from the carnage at the theater, though the trap was never sprung, they testified.

Holmes showed less focus after police arrested him as he stood outside the theater, clad in body armor. He played with the paper bags they placed on his hands to preserve gunpowder evidence, pretending they were puppets, Aurora Det. Craig Appel testified. Holmes tried to jam a staple into an electrical outlet.

On Tuesday, the case was dominated by the litany of Holmes' preparations. Law enforcement officers said Holmes' first recorded purchase was of two tear gas grenades, ordered online May 10.

Holmes also bought two Glock handguns, a shotgun and an AR-15 rifle, along with 6,295 rounds of ammunition, targets, body armor and chemicals, prosecutors said. The magnitude of the attack was captured in the first 911 call, played Tuesday in court, that police said recorded at least 30 shots in 27 seconds.

He dyed his hair bright orange, then bought a scope and non-firing dummy bullets on July 1, the visit and the new hair color documented in security video.

Finally, he purchased glycerin and potassium permanganate - chemicals that could combine to create fire - from a Denver science store. At some point, he also improvised napalm, as well as thermite, a substance which burns so hot that water can't extinguish the blaze.

Holmes' purchases were for two planned attacks, prosecutors said - the theater shooting and the booby-trapped apartment that would have blown up if anyone had entered.

The bottle of glycerin was meant to fall into the permanganate when the door to his apartment opened, to cause an explosion and then a fire, prosecutors said.

Parts of Holmes' carpet were soaked with gasoline and oil, and ammonium chloride, a white powder, was poured onto the floor in strips, FBI bomb technician Garrett Gumbinner said.

"It would have ignited and the whole apartment would have exploded or caught fire," Gumbinner said.